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Sulfur Passivation of Interface between Aluminum Oxide and Silicon Germanium

Abstract

It is well known that silicon germanium (SiGe) is a promising candidate for next generation complementary metal-oxide-semiconductor (CMOS) integrated-circuit (IC) with the advantage of having high electron-hole mobility compare to silicon (Si). The high-k materials are commonly been used for scaling down the gate oxide. However, the passivation strategies between SiGe and high-k gate oxide still need to be understood since the native oxide on the SiGe surface will cause the interface defects and effect the device quality. In the thesis, aluminum oxide (Al₂O₃) had been deposited on SiGe (001) substrates by atomic layer deposition (ALD). To minimize the defect density between Al₂O₃ and SiGe, two wet clean recipes with HF and HF plus (NH₄)₂S had been developed to both remove the native oxide and chemically passivation SiGe surfaces. Based on cleaning recipes, two studies were performed, one on the effect of ALD temperature on quality on Al₂O₃/SiGe interfaces and the other, on air stability of SiGe surfaces with different wet clean recipes prior to ALD. Al₂O₃/SiGe interfaces were characterized electrically by capacitance-voltage (C-V) spectroscopy and chemically by angle-resolved X-ray photoelectron spectroscopy (AR-XPS). It has been shown that low-temperature ALD processes have the ability to attain a high interface quality with lower density of interface and border traps. Both cleaning methods led to good air stability up to an hour, extending the viable manufacturing queue time. In addition, sulfur treatment suppressed GeOx formation and increased Al₂O₃ nucleation density on SiGe surfaces, which led to lower leakage current while achieving the record equivalent oxide thickness (EOT) of 2.0nm for Al₂O₃/SiGe devices

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